One of the major foci in cell biology is to understand the process of nuclear division. In each cell cycle the chromosomes must be faithfully replicated and the complex nuclear structure has to be duplicated and reorganized. Intensive research has been directed towards identifying the signal transduction pathways and molecules involved in the complex and dynamic events required for mitosis and cell division. This research has demonstrated that many of the molecules playing important roles in control of the cell cycle are protein kinases. Of particular medical significance is the finding that many cancers appear to stem from alterations in such cell cycle regulatory molecules which lead to genomic instability and tumorigenesis, and these molecules are highly evolutionary conserved. Thus the study of mitosis and cell division in various species promises to help elucidate general principles governing cell division which apply to humans as well. The object of this proposal is to clone and analyze the molecular structure and functional biology of a novel nuclear protein (p2Ab17) in Drosophila melanogaster which shows a dynamic cell cycle-specific distribution pattern and shares homology with serine-threonine kinases related to the raf family of oncogenes. This protein was first identified immunocytochemcally using monoclonal antibody 2A. The proposed experiments are designed to elucidate structural and biochemical features of the p2Ab17 protein, which co-localizes with the mitotic apparatus and chromosomes at metaphase and with chromatin or the nuclear matrix at interphase, and to determine the role p2Ab17 may play in signal transduction processes involved in nuclear division. Drosophila embryos provide an especially advantageous model system for these studies due to their synchronous early syncytial cleavage pattern which can be readily investigated using molecular, cell biological, and genetic approaches. We will apply these techniques in order to initiate a study of regulatory controls for nuclear division and to determine the functional role of p2Abl7 during mitosis. Since cancer could be viewed as a disease of the signaling system that controls cell proliferation and differentiation, understanding the roles of such signaling molecules in mitosis during normal Drosophila development will yield important insight into how they may function in both normal and cancerous cells in humans.